Traditional web feed printing processes have used a series of expensive mechanical rollers and counterbalancing components to assist in controlling movement of printable medium through printing units. Mechanical systems experience wear and require ongoing monitoring and regular maintenance. It is desirable to have sensor and microcontroller operation instead. Further, the control model should be generalized. A control model, for alternating between single sheet printable medium and continuous printable medium, is seen in U.S. Pat. No. 5,214,750. It defines modes of operation and the flow control of motors. That control system is application specific, not generalized.
In the industry today, products aimed at label printing are identified as dedicated printers. They generally use web printing processes, continuous roll printable medium feedstock, and have been designed specifically for label printing. Label printing occurs in two stages, with the first pass for logos and background material. A second stage is used to print job specific data like prices, SKUs (stock keycodes), barcodes or promotional materials. Likewise, point of sale printers are recognized as dedicated devices, aimed at printing receipts and records of transactions.
Dedicated printers may be larger laser printers or smaller point of sale thermal or ink jet printers, as disclosed in U.S. Pat. Nos. 6,474,883 and 6,343,884, respectively. In both cases, the degree of integration between the print engine and the printable medium feed mechanisms is very high. A print engine generally has printer heads and conveying mechanisms to move printable medium or other print media. The print engine and its continuous printable medium feeder mechanism cannot be decoupled in these two cases. The feeder mechanisms do not have independent operating capabilities, suited to readily adapt to an entirely different print engine.
One instance of a feeder that is somewhat separate from a print engine is seen in U.S. Pat. No. 7,165,741. In this case an external cartridge is attached to the body of a print engine and efforts are made to position printable medium and control rattling of printable medium. The printable medium positioning is manual and, therefore, prone to error or possible damage of the media end. Rattling of printable medium may be better controlled through appropriate tensioning of printable medium and some minimal guidance.
To summarize, some of the shortcomings of existing technology include the use of mechanical web guides or single purpose control mechanisms, rather than generalized control systems. Another shortcoming is the tight coupling between print engines and feeder mechanisms which does not allow easy adaptation of the feeder mechanism to an entirely different print engine. More independent print media cartridges have manual printable medium or media positioning, which is prone to inaccuracy.